Method and device for determining the ion flow in internal combustion engines

ABSTRACT

A method for processing the ion flow signals of internal combustion engines by offset correction, masking and multiplexing for engine control functions wherein, after the measurement of the ion flow signal in each cylinder for the purpose of offset correction in advance of each ignition operation, the level of the measurement signal of the cylinder is detected; during masking operation, the measurement signal is substituted in a second signal by the level value and is subtracted from the second signal until the next ignition operation and thereafter, the channels which are to be multiplexed, are combined to a third signal by the addition of the second signals of the particular cylinders, the second signal being derived from the measurement signal.

FIELD OF THE INVENTION

An ionization of the participating gases takes place because of chemicaland physical processes during combustion. A current can be measured whena voltage is applied to two electrodes which project into the gas andare insulated from each other. This is characterized in the following asan ion flow.

BACKGROUND OF THE INVENTION

This phenomenon can also be observed in internal combustion engines suchas in spark-ignition engines. For some time, it has been attempted toutilize the ion flow for various engine control and diagnostic functionssuch as for knock detection, misfire detection, phase detection,estimation of combustion pressure or the position of the pressuremaximum, determination of the mixture composition and for detection ofthe lean running limit.

The spark plug is usually used as a measuring probe. After applying avoltage across the center electrode and ground, the ion flow can bemeasured after the decay of the ignition spark.

With respect to the above, the following problems occur: a currentoffset occurs because of the shunt resistances outside and within thespark plug (for example, contamination of the spark plug insulator).This current offset interferes with an exact detection of the ion flowgenerated by the combustion and this offset is to be eliminated.

No ion flow measurement is possible during the burning duration of theignition spark. A masking can lead to signal jumps in the ion flowmeasurement signal which, for example, leads to erroneous detections ina subsequent knock detection. The ignition process should be maskedwithout disturbing the measurement signal.

Methods and components realized in analog technology, such as short-termintegrators, or methods and components realized in digital technologyare applied to evaluate the ion flow. It is conventional to switch themeasurement signals of several cylinders sequentially to these resourcesin order to save cost (multiplexing). The multiplexing has to beexecuted without crosstalk between the cylinder channels. Furthermore,it is to be prevented that the now shorter signal segments, which arespecific to a cylinder, lead to a reduction in quality when making theoffset correction. The improvement of the reliability and the robustnessof engine control functions and diagnostic functions is achieved byutilizing these signals with improved signal to noise ratio for thefeature formation.

SUMMARY OF THE INVENTION

The object of the invention comprises providing a method which solvesthe above problems.

The invention is for a method and an arrangement for processing the ionflow signal of an internal combustion engine by offset correction,masking and multiplexing for engine control functions. An embodiment ofthe method of the invention includes the steps of: measuring the ionflow signal in each cylinder during an ignition operation to provide ameasuring signal; then detecting the level value of the measurementsignal of the cylinder for the purpose of offset correction; deriving asecond signal from the measurement signal; during the masking,substituting the measurement signal in the second signal by the levelvalue and subtracting the measurement signal from the second signaluntil the next ignition operation; and, then combining the channels tobe multiplexed into a third signal by adding the second signals of thecylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

The method of the invention and the arrangement of the invention fordetecting the ion flow in internal combustion engines is explainedhereinafter with respect to an embodiment with reference being made toFIGS. 1 to 6.

The relationship of the method and the arrangement to the technicalbackground is made clear in FIG. 1 in the form of a block diagram.Specific configurations of the essential signal processing blocks areexplained in greater detail in FIGS. 2 to 4 while including signalexamples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The complete signal processing chain is shown in detail in FIG. 1. Thecombustion process 2 is at the start of this chain and is initiated bythe ignition 1. An ionization takes place in the combustion chamber fora proper mixture combustion. The means 3 functions to generate andmeasure an ion flow signal s1 which permits conclusions to be drawn asto the ionization process during the mixture combustion. Means 4 followsmeans 3 and the masking according to the invention and the offsetcorrection of the ion flow signal takes place in means 4. The ion flowsignals s2 from different cylinders are advantageously combined to asummation signal s3 with the aid of a multiplexing unit 5. Theconditioning of the signal s3 in accordance with the invention makespossible the use of the same in addition to misfire detection also forfurther applications 9 such as knock detection.

A computer supported further processing is advantageous for the signalevaluation. A unit 6 can be used for the conversion of thetime-continuous and value-continuous ion flow signal s3 into a digitalsignal sequence s4. The unit 6 includes an antialiasing filter 6.1 andan analog/digital converter 6.2. From the digital signal sequence s4, afeature former 7 extracts feature vectors s5 which are specific to acylinder. The detection of the combustion misfires takes place in thedownstream classifier 8 on the basis of these feature vectors s5. Acontrol unit 10 is needed for the time-dependent drive of the ignition 1as well as for the time-dependent drive of the means 4 of the inventionfor offset correction and masking.

FIG. 2 shows the method of the invention for the offset value correctionand for the ignition spark masking of the ion flow signal s1 generatedwith the aid of means 3. For this purpose, the signal s1 c is generatedin a first step from the signal si in such a manner that the signal s1is passed through within a defined measurement window region and isconverted to a constant substitute value s1 b outside of thismeasurement window region. Especially, the portion of the ignition sparkin the ion flow si is substituted with this substitute value s1 b. Thesubstitute value s1 b should then correspond in order of magnitude tothe residual offset of the ion flow signal s1. For this purpose, thesubstitute value s1 b is determined for each cycle individually shortlybefore the ignition process by means of a scan hold circuit 4.2.Advantageously, the ion flow signal s1 is not directly accessed for thedetermination of the holding value s1 b; instead, access is made to adisturbance corrected signal s1 a. The disturbance correction of thesignal s1 can, for example, take place with an adapted filter 4.1. Theoutput signal s2 finally results by subtraction of the substitute values1 b from the ancillary signal s1 c. This output signal s2 ischaracterized in that it is without discontinuity and is corrected ofignition influences as well as of a current offset caused by shunts.

In FIG. 3, the downstream signal multiplexing 5 is shown. Because of thespecial characteristic of the cylinder-individual signals of the type ofs2, the signals of several cylinders can be combined to a common signals3 in the form of a time-dependent multiplexing. A mutual influencing ofthe multiplexed signals is precluded because of the measurement windowsubstitution provided in 4. In this way, the resource complexity for thesignal transmission and the subsequent digitalization is greatlyreduced.

A filter 6.1 can be switched into the signal path forward of theanalog-to-digital converter 6.2 in an advantageous manner. By acorresponding configuration of this filter, the possibility is presentthat signal s3 can be adapted especially to low scanning rates. Adiscrete signal sequence s4 is available at the output of theanalog-to-digital converter 6.2.

With the aid of the feature former 7, feature vectors s5 individual toeach cylinder are formed from the signal s4. In FIG. 4, a possiblerealization of the feature former is shown as an example.

First, the continuous data current s4 are split into componentsindividual to the cylinders with the aid of means 7.1. In a very simpleembodiment, a two-dimensional feature vector can be formed for eachcylinder-individual combustion cycle. This two-dimensional featurevector comprises the ion flow maximum value and the short-time integralover the ion flow measurement window. A downstream classifier 8 candistinguish regular combustions from combustion misfires based on thefeature vectors s5 by a comparison to correspondingly computed thresholdvalues.

Based on the method shown above, an alternative method can be used whichis explained in greater detail with respect to FIGS. 5 and 6.

This alternative method replaces the means 3, 4, 5 and 10 described inFIG. 1 and uses the signal from the combustion process 2 and supplies asignal s8.3 which is processed in accordance with the invention in thesame manner as signal s3.

In the first step according to the invention, an ion flow is selected inthe selector unit 8.1 from several ion flows from different cylinders inan advantageous manner. This ion flow signal is measured with means 8.2before it is subjected in means 8.3 to the offset correction of theinvention and the masking of the ignition spark. The masking of theignition spark and the offset correction are shown in FIG. 6.

Before means 8.1 changes the selection of the ion flows, a switchover toa constant value is made with means 8.3.5. This constant value is fixedpreviously in accordance with the invention and does not permit adiscontinuity in the signal s8.3. During this masking, a new offsetvalue is first formed with the means 8.3.1 and 8.3.2. This new offsetvalue is subtracted from the original signal from means 8.2 via means8.3.4. The determination of the offset value is completed in accordancewith the invention before the ignition spark can be seen in the ion flowsignal. The disturbance correction of the signal from the combustionprocess 2 can, for example, take place with an adapted filter 8.3.1. Ifthereafter, the influence of the ignition spark on the ion flow signalis at an end, then there is a switchback with means 8.3.5 to the outputof the means 8.3.4. The determined value from means 8.3.1 is held in thescan hold circuit 8.3.2 until the next switchover of means 8.3.5 and 8.1so that an offset-corrected and disturbance-corrected signal s8.3 ispresent after means 8.3.5 for further processing in means 6. A controlunit 8.4 is necessary for the time-dependent control of the means 1,8.1, 8.2 and 8.3.

What is claimed is:
 1. A method of processing an ion flow signal of aninternal combustion engine, the method comprising the steps of:selecting a cylinder of said engine for ion flow measurement and formingan ion flow signal; forming an offset value for said cylinder andsubtracting said offset value from said ion flow signal; masking theignition spark and masking the switchover of the cylinder which tookplace previously for making an ion flow measurement and an offsetcorrection with a previously fixed constant value; and, processing thissignal as a third signal.
 2. An arrangement for processing an ion flowsignal of an internal combustion engine, the arrangement comprising:means for selecting a cylinder of said engine for ion flow measurementand forming an ion flow signal; means for forming an offset value forsaid cylinder and subtracting said offset value from said ion flowsignal; and, means for masking the ignition spark and masking theswitchover of the cylinder which took place previously for making an ionflow measurement and an offset correction with a previously fixedconstant value.
 3. A method for processing the ion flow signal of aninternal combustion engine by offset correction, masking andmultiplexing for engine control functions, the method comprising thesteps of: measuring the ion flow signal in each cylinder during anignition operation to provide a measuring signal; then detecting thelevel value of the measurement signal of the cylinder for the purpose ofoffset correction; deriving a second signal from said measurementsignal; during said masking, substituting said measurement signal insaid second signal by said level value and subtracting said measurementsignal from said second signal until the next ignition operation; and,then combining the channels to be multiplexed into a third signal byadding the second signals of said cylinders.
 4. The method of claim 3,wherein the signal, which is so prepared, is further processed by amethod for knock detection.
 5. The method of claim 3, wherein thedetected level values, which characterize the offset current, makepossible a diagnosis of the ignition system and of the condition of thespark plug (spark plug contamination) by a comparison to fixed oroperating-state dependent threshold values.
 6. The method of claim 3,wherein a first feature arises from short-term integration of the thirdsignal within a measurement window assigned to the individual cylindersand this first feature makes a misfire detection possible by comparisonto fixed or operating-state dependent threshold values.
 7. The method ofclaim 3, wherein the third signal is subjected to a lowpass filteringand analog-to-digital conversion and is used in a suitable microcomputeras the basis of further engine control functions.
 8. The method of claim3, wherein the misfire detection is carried out in accordance with thedigitalization in the microcomputer.
 9. The method of claim 3, wherein asecond feature arises from a maximum value evaluation of the thirdsignal within the measurement windows assigned to the individualcylinders; and, the second feature makes a misfire detection possiblevia a comparison to fixed or operating-state dependent threshold values.10. The method of claim 9, wherein both features are used in atwo-dimensional feature space to detect misfires.
 11. An arrangement forprocessing the ion flow signal of an internal combustion engine byoffset correction, masking and multiplexing for engine controlfunctions, the arrangement comprising: measuring means for measuring theion flow signal in each cylinder during an ignition operation to providea measuring signal; detecting means for detecting the level value of themeasurement signal of the cylinder for the purpose of offset correction;means for deriving a second signal from said measurement signal; meansfor substituting said measurement signal in said second signal by saidlevel value and subtracting said measurement signal from said secondsignal until the next ignition operation; and, means for combining thechannels to be multiplexed into a third signal by adding the secondsignals of said cylinders.
 12. The arrangement of claim 11, wherein thesignal, which is so prepared, is further processed by a method for knockdetection.
 13. The arrangement of claim 11, wherein the detected levelvalues, which characterize the offset current, make possible a diagnosisof the ignition system and of the condition of the spark plug (sparkplug contamination) by a comparison to fixed or operating-statedependent threshold values.
 14. The arrangement of claim 11, wherein afirst feature arises from short-term integration of the third signalwithin a measurement window assigned to the individual cylinders andthis first feature makes a misfire detection possible by comparison tofixed or operating-state dependent threshold values.
 15. The arrangementof claim 11, wherein the third signal is subjected to a lowpassfiltering and analog-to-digital conversion and is used in a suitablemicrocomputer as the basis of further engine control functions.
 16. Thearrangement of claim 11, wherein the misfire detection is carried out inaccordance with the digitalization in the microcomputer.
 17. Thearrangement of claim 11, wherein a second feature arises from a maximumvalue evaluation of the third signal within the measurement windowsassigned to the individual cylinders; and, the second feature makes amisfire detection possible via a comparison to fixed or operating-statedependent threshold values.
 18. The arrangement of claim 17, whereinboth features are used in a two-dimensional feature space to detectmisfires.